diff --git a/header.go b/header.go
index 42ec928..e5c2cec 100644
--- a/header.go
+++ b/header.go
@@ -106,6 +106,22 @@ func (i Importance) NumString() string {
 	}
 }
 
+// XPrioString returns the X-Priority number string based on the Importance
+func (i Importance) XPrioString() string {
+	switch i {
+	case ImportanceNonUrgent:
+		return "5"
+	case ImportanceLow:
+		return "5"
+	case ImportanceHigh:
+		return "1"
+	case ImportanceUrgent:
+		return "1"
+	default:
+		return ""
+	}
+}
+
 // String returns the importance string based on the Importance
 func (i Importance) String() string {
 	switch i {
diff --git a/msg.go b/msg.go
index e17fc33..2b391b6 100644
--- a/msg.go
+++ b/msg.go
@@ -308,7 +308,7 @@ func (m *Msg) SetImportance(i Importance) {
 	}
 	m.SetHeader(HeaderImportance, i.String())
 	m.SetHeader(HeaderPriority, i.NumString())
-	m.SetHeader(HeaderXPriority, i.NumString())
+	m.SetHeader(HeaderXPriority, i.XPrioString())
 	m.SetHeader(HeaderXMSMailPriority, i.NumString())
 }